It was a solid 8 in the first half of the drama because of the witty, on point humor. But then it turned into your typical murder crime drama, with dumb leads to boot, which became more apparent as episodes went on. So, of course, many people died before the culprit was caught and even that was through sheer luck and out of the grave help of a single smart side character. Some deaths could have even be prevented if characters weren't acting atrociously dumb, especially near the end of the drama. It was frustrating to watch how clumsily it was resolved.
The culprit wasn't revealed too early as it often happens in such dramas, which is nice, but showrunners did start giving heavy hints in late episodes and after most of the suspects were killed not many characters were left to suspect anyway. The motive was very meh, considering that the culprit character didn't give any serial killer vibes until he was caught and there was no sus behavior in his past.

I also didn't like that for a few episodes the drama veered into a side story that basically lead to nowhere. I'm talking about FL mother's and assemblyman's story - a sudden end, no justice for those who got killed and cheated of their money. And then this story was promptly swept under a rug. Left a feeling of it being a filler.

And lastly, I didn't like that showrunners decided to shoehorn sudden romance between ML and FL in like 1.5 episodes left to go. Was completely unnecessarily and at that point felt unbelievable. And I guess FL wasn't really into SML, even though she was running after him and making googly eyes at him like a stupid cow for most of the drama.

And here's a list of very stupid things that went on at the end of the drama that made me lower the score:
-FL has several victims' blood on her hands.
She could have saved the cafe waitress in the field by asking the whole bus for help. The culprit was among them, but he wouldn't have been able to kill the victim with a crowd around.
She could have saved the assemblyman and her grandpa as well by telling the police she saw the culprit in exact same raincoat, with exact same knife about to backstab the assemblyman. But she dismissed that he might have been the actual killer by listening to his sappy lie. Lolwut, woman? Not to mention that no matter what his intentions were, serial or not, he was about to stab a man!
And last victim is SML. Because of her stupid irresistible desire to meet him no matter what time of day it is and that a serial killer is on the loose, she agreed to meet with him late at night far away from residential houses, and without telling ML. Then, even though she said she believed him, she of course ran away from him when he ran after her to show her the murder knife.

-FL also was made frustratingly very dumb near the end of the show in general. Walking at night alone, being uncooperative because her love interest may be the killer, slapping ML and blaming him (serious wtf moment) for so many victims, the list goes on...At least in the end she apologized to ML.

-ML should have arrested SML for the farmer's death right then and there after he saw blood on his hand and because SML's house was very close to where ML lost the killer. But instead ML let him go and let that rare, concrete evidence, with no psychic mumbo jumbo, go to waste. That was very dumb on ML's part.

-SML's behavior throughout the drama was very frustrating as well. One can say that it was his suspicious, antagonistic, secretive and uncooperative behavior that got him killed in the end. He may have been smart to figure out the killer first, but his aloofness and inability to trust people didn't help his case whatsoever.

-The farmer with psychic powers was basically asking for it. Ffs, why'd you be grabbing a leg of a person you strongly suspect to be the killer in the middle of the night in a remote area?

So considering all of the above I can't give it more than 7.0. The humor was funny and memorable though, while it lasted.